1. Field of the Invention
This disclosure is related to the field of devices and methods used to monitor fermentation. Specifically, this disclosure is related to devices and methods which are used to measure the percentage Alcohol By Volume (% ABV), specific gravity or sugar content of a fermented liquid.
2. Description of the Related Art
Fermentation is the process of live yeast cells acting on simple sugars dissolved in a liquid, producing ethanol, carbon dioxide gas, and trace amounts of other compounds. It is a process used in the making of beers, wines, and spirits by the chemical conversion of sugars into ethanol.
Certain alcoholic beverages, like beer and wine, are produced by fermenting sugars dissolved in water (called wort in beer, must in wine) using special strains of yeast. Brewers and wine makers generally monitor the progress of the fermentation process by measuring the fermenting beverage's specific gravity, or relative density compared to water, of the liquid at various stages in the fermentation process. Generally, a fermenting liquid's specific gravity is measured by manually taking small samples from the fermentor at periodic intervals and measuring the sugar content (in units called Brix, Plato, or Balling). Generally, wine makers traditionally use ° Brix, while brewers use ° Plato. ° Balling is the old unit used by brewers which has largely been replaced by ° Plato. Notably, all three units represent nearly the same values and can be used interchangeably.
Devices which are utilized in the art to take this manual measurement of a fermenting beverage's specific gravity include hydrometers, refractometers, pycnometers and oscillating U-tube electronic meters. A hydrometer, one of the devices most commonly utilized to measure the specific gravity of a liquid, generally works as follows. The hydrometer is a device of a generally constant weight that displaces different volumes of liquid as the liquid's density varies. Accordingly, the typical hydrometer consists of a weighted bulb with a slender graduated stem rising above it. Once the bulb is submerged, the increment of displacement with the depth is determined by the cross section of the stem, which is generally very small to ensure a high degree of accuracy.
The measured specific density of a fermenting liquid will be largely dependent on the sugar content of the fermenting liquid. During the fermentation process, yeast in the liquid converts sugars into carbon dioxide and alcohol. The decline in the sugar content of the liquid and the increase in the presence of ethanol (which is less dense than water) drop the density of the fermenting liquid—i.e., there is an inverse relationship between the specific gravity measurements and the amount of ethanol present in the fermenting liquid. The percentage of alcohol in the fermenting liquid can be calculated from the difference between the original specific gravity of the fermenting liquid and the current specific gravity of the fermenting liquid. By monitoring the decline in the specific gravity over time, the brewer obtains information on the health and progress of the fermentation and determines that it is complete when the gravity stops declining. When the fermentation is complete, the current specific gravity is then called the final gravity. Notably, when monitoring the progression of fermentation by specific gravity measurement, carbon dioxide bubbles may have to be drawn out of the liquid sample with a vacuum in order to get accurate specific gravity measurements. In certain instances, it might even be necessary to halt fermentation in the liquid sample in order to prevent continued carbon dioxide production.
From the measurement of specific gravity, ° Brix can be approximated as:Brix=261.3×(1−1/g),  [Eq. 1]
where:
g is the specific gravity of the solution at 20° C.
As noted previously, during the course of the fermentation, the specific gravity value drops while the amount of ethanol rises; in fact, the relationship is almost linear and can be approximated as follows:% Alcohol by Volume(% ABV)=(O.G.−C.G.)×133.3,  [Eq. 2]
where:
O.G. is the original specific gravity (before fermentation begins), and
C.C. is the current specific gravity.
When the fermentation is complete, the current gravity is called the final gravity and is designated F.G. In a typical pale ale, for example, the O.G. might be around 1.050 and the F.G. about 1.012; using Eq. 2 above, the % ABV of the finished beer would be approximately 5.1 percent.
There are several reasons why brewers and wine makers monitor the progress of their fermentations. The most common reason is to determine when the primary phase of the fermentation is complete (or nearly complete) and know when the product is ready to move to the next phase. Brewers typically transfer the beer from the fermentor to what is called a bright beer tank or lagering tank, where the beer is conditioned—and sometimes carbonated—for a time before it is packaged. Another reason to monitor specific gravity is to look out for any abnormalities—e.g., for a particular recipe using a healthy, standard yeast strain in a high quality wort, unless something is out of the ordinary, fermentation should progress in a well-behaved, repeatable fashion.
While it is the traditional methodology utilized in the fermented beverage industry, there are numerous problems with monitoring the progress of fermentations via manual specific gravity measurements. One major problem with the manual method of determining the specific gravity of a fluid is contamination. Every time you open the fermentors you are risking infection from airborne microbes. Once contamination reaches the fermenting liquid, the batch is generally ruined and must be discarded. Further, the current processes utilized in the art are manual, cumbersome, prone to human error, and often erratic and unreliable. Finally, due to their labor-intensive nature and the risk of infection, the currently utilized processes fail to adequately assess the progression of fermentation as the specific gravity measurements are only taken at intermittent periodic intervals. Stated differently, because the manual progress is so cumbersome and at-risk for contamination, only a few specific gravity measurements are taken during this fermentation process. This creates a very imprecise tool to measure the health and progression of the fermentation. Accordingly, if something unexpected happens during the fermentation (e.g., the yeast dies or is rendered ineffective), it is not often detected until it is too late to save the fermenting liquid.